The present invention relates to a gearbox head for a motor-driven, manually guided implement for driving a cutting tool.
Such a gearbox head for an implement having a rapidly rotating cutting tool, for example in conjunction with a brushcutter, trimmer or edger, is formed with a housing having minimal exterior dimensions. Disposed in the gearbox head housing for driving the cutting tool is a planetary gear arrangement that is preferably embodied as a bevel gearing. Such a bevel gearing is lubricated by a lubricant filling that is provided in the housing. Such a gearbox head effects an adaptation of the speed of the drive motor to the cutting tool along with an appropriate positioning of the cutting tool on the manually-guided implement. In order, during operation of the manually-guided implement, to provide a pressure equalization between the interior and the exterior of the gearbox head, a channel is provided in a gear shaft of the planetary gear arrangement, or an appropriate groove is provided in a bearing seat for a shaft of the planetary gear arrangement.
Since during operation of the gearbox head operating temperatures of greater than 100xc2x0 C. can occur due to the high speeds, an increase in pressure is effected in the gearbox head that must be compensated for via the channel. With heretofore known gearbox heads, lubricant can enter the pressure equalization channel and can lead to losses of lubricant. As a result, it is necessary to refill the gearbox head with lubricant.
It is therefore an object of the present invention to improve a gearbox head of the aforementioned general type in such a way that it is possible to have a long lasting operation of the gearbox head without requiring maintenance.